The present invention relates to a magnetic carrier in powder or particle form used in electrophotographic development equipment, and, more particularly, to an environmentally benign manganese oxide, iron oxide carrier having titanium dioxide or titanium oxide added thereto to control magnetic brush properties of the carrier.
Carriers in the form of powder or particles are used to transfer toner in many types of electrophotographic development equipment or reprographic equipment. For example, such powders are used in copying machines and laser printers. Typically such carriers are ferrite powders that consist of iron oxide in combination with various metal oxides such as nickel, zinc or copper among others. Patents have been issued directed to various ferrite carrier compositions including the following: U.S. Pat. Nos. 4,623,603, Timura et al.; 4,85,162, Honjo et al.; 4,898,801, Tachibana et al.; 4,485,162, Imamura et al.; and 3,929,657, Jones. Such prior art patents teach both single component and dual component ferrite carriers. These patents also teach various crystalline structures for the carriers. These patents also teach the utilization of compositions of ferrites with various metals and various processes for the manufacture of such carriers.
The need to provide environmentally benign carriers which may be safely and easily recycled or disposed following use is a growing prerequisite design consideration for electrophotographic development equipment. Currently many compositions which are used as carriers, contain elements that might be regarded as hazardous to the environment. The proposed invention concerns a composition which does not present the environmental concerns of many currently available carriers.
It is also known that when an iron oxide carrier is selected for electrophotographic magnetic brush development, the electrical conductivity and the magnetic properties of the carrier are important and parameters are often established for desired development characteristics. Additionally, carriers are often coated with various polymer resins selected for compatibility with specific toners. Polymer coatings are known to typically reduce the conductivity or increase the resistivity of the carriers. Conductive additives such as carbon black may also be added to coatings to increase the conductivity or lower the resistivity of carriers. However, coatings on carrier surfaces wear or erode and subsequently are transferred onto the copied or printed documents along with the toner. Black toner applications typically do not show adverse effects resulting from the transfer of additives. However, the image quality from color toner applications, which are becoming more and more popular, can be adversely affected. The color toner applications for magenta, cyan and yellow thus may be adversely affected in many circumstances and so there has developed a need to provide an environmentally benign iron oxide or ferrite carrier particle or core which maintains an appropriately high conductivity prior to coating and which can simultaneously offer a range of magnetic values useful in magnetic brush developer systems particularly for color reprographics.